Fluid control valve

ABSTRACT

A piezoelectric fluid control valve (10) and fluid control method using a polymorph (48) with a characteristic that as a potential difference is applied thereto, the polymorph is deflected. The valve includes a supply port (14) for introducing fluid and a chamber (16) defined within the valve body. An outlet port (18) is in fluid communication with the chamber and a device controlled thereby, such as an anti-lock brake system. A relief port (78) returns fluid to a source thereof. Upper and lower metering elements (100, 116) are supported within the chamber. A cantilevered spring valve (128, 130) is positionable within metering orifices defined within the metering elements (100, 110). The polymorph is positioned between and in operative communication therewith. An electrical circuit (56) is connected to the polymorph, the circuit providing the potential difference thereto, which is regulated in accordance with an input signal delivered to the circuit. An input signal generator (58) operates in response to a sensed condition such as brake pressure and wheel deceleration, the fluid flow in the outlet port being continuously modulated in response to the sensed condition.

REFERENCE TO APPLICATION

This is a divisional application of application Ser. No. 08/163,212filed on Dec. 6, 1993, now U.S. Pat. No. 5,445,185, which is acontinuation-in-part of application Ser. No. 08/043,127, filed Apr. 5,1993, now U.S. Pat. No. 5,267,589.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is concerned with piezoelectric fluid controlvalves. More specifically, the invention relates to a valve used inconjunction with a system, such as an anti-lock braking system, whichrequires high frequency actuation capabilities.

2. Background Art

The piezoelectric effect was discovered by Jacques and Pierre Curie in1880. They found that certain materials deform when exposed to anelectrical field. This has become known as the inverse piezoelectriceffect. The effect is practically linear, i.e., the deformation variesdirectly with the applied potential difference. It is alsodirection-dependent, so that if the material is exposed to an electricfield, it will experience an elastic strain which causes its length toincrease or decrease according to the polarity of the field. Thisbehavior is manifest in such materials as piezoelectric ceramics, whichare hard, chemically inert, and completely insensitive to humidity andother atmospheric influences.

As an example of harnessing piezoelectric phenomena, U.S. Pat. No.4,690,465, which issued on Sep. 1, 1987, discloses an anti-skidhydraulic pressure modulator for a vehicular hydraulic braking system.The system includes a piezoelectrically operated pressure modulator,including a passage which is opened and closed by a piezoelectricactuator. The piezoelectric element expands and contracts almostinstantaneously in response to voltage application and voltage drop.However, in such systems, responsiveness is limited in operation by ashut-off valve being positioned either in an "on" or "off" position.Such systems do not exhibit a continuously controlled modulation.

In the past, the effectiveness of devices which may be controlled by apressure control valve has been limited by the inherent sluggishness ordelay with which fluid flow, for example, changes in response to asensed condition (such as applied brake pressure) .

In an article entitled. "Electrically Activated, Normally-ClosedDiaphragm Valves" by H. Jerman (91CH2817-5/91 IEEE), the author observesthat conventional valves for flow control have typically used magneticactuation in the form of solenoids or motors to drive spool valves. Thereference notes that valve actuation is possible using piezoelectricdrivers, but the properties of such materials produce high forces with avery small deflection for button-type actuators. The reference statesthat such a driver has been reported as a valve actuator, but thecomplicated assembly and high voltage operation is said to beunattractive for many commercial applications.

U.S. Pat. No. 4,768,751 which issued on Sep. 6, 1988 discloses a siliconmicromachined non-elastic flow valve. That reference discloses a valveassembly for controlling fluid flow, including an actuator and a fluid.The actuator separates the nozzle plate from a valve plate, therebypermitting fluid flow. Also disclosed is a spring means for biasing thenozzle plate into a closed position to arrest fluid flow.

Against this background, there remains an unsatisfied need for low costfluid control valves which can be made in large quantities and whichexhibit a higher frequency response than those presently known, whereinthere is a continuous modulation of flow output in response to an inputsignal which is communicated to the valve.

SUMMARY OF THE INVENTION

The present invention is a piezoelectric fluid control valve fordelivering a fluid, such as hydraulic fluid, to a device such as ananti-lock braking system, which is operable in response to fluidemerging from the valve.

Included in the valve is a polymorph which includes one or morepiezoelectric plates or ceramic wafers. The polymorph has thecharacteristic that as a potential difference is applied, it becomesdeflected.

The piezoelectric fluid control valve of the present invention comprisesa valve body with a supply port for introducing fluid into the valve, achamber defined therewithin, and an outlet port which is capable ofdelivering fluid to the device controlled thereby.

An upper metering element is supported within the chamber. The uppermetering element lies adjacent to the polymorph. Located on an opposingface of the polymorph is a lower metering element.

Each metering element has an anchored end affixed to a wall of thechamber. An inlet channel is defined in communication with the supplyport within the anchored end of the upper metering element. An outletchannel in communication with the return port is defined within thelower metering element.

Each metering element has a rectangular metering orifice whichcooperates with a cantilevered spring valve that is positionabletherewithin. The cantilevered spring valves are continuouslydisplaceable between an opened position and a normally closed position.

The polymorph, positioned between and in operative communication withthe upper or lower metering elements, has the characteristic that aspotential difference is applied, it becomes deflected, therebydisplacing the upper or lower cantilevered spring valve in response toan electrical signal provided thereto. The electrical signal isgenerated in response to a sensed condition, such a brake pressureand/or wheel deceleration. As a result, fluid in the outlet port iscontinuously modulated in response to the sensed condition.

It is an object of the present invention to provide a fluid controlvalve which exhibits a higher frequency response than presently known.

It is also an object of the present invention to provide continuousmodulation of fluid flow or pressure in a linear relation with the inputsignal communicated to the valve.

Further, it is also an object of the present invention to provide a lowcost, fluid control valve having fewer moving parts which can be made inlarge quantities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an embodiment of apiezoelectric fluid control valve according to the present invention;

FIG. 2 is a cross-sectional view of another valve embodiment,illustrating the valve in its closed position;

FIG. 3 is a cross-sectional view of the valve depicted in FIG. 2, takenalong the line 3--3 thereof;

FIG. 4 is a cross-sectional view of an alternate embodiment of thepresent invention, illustrating the valve in an opened position;

FIG. 5 is a cross sectional view of a valve in accordance with a thirdembodiment, illustrating the valve in its opened position wherein fluidis delivered to a device controlled thereby;

FIG. 6 is a cross sectional view of the third embodiment of FIG. 5,illustrating the valve in a dump position;

FIG. 7 is a cross sectional view of the third embodiment of FIG. 5,illustrating the valve in a closed position;

FIG. 8 is a top view of the valve depicted in FIGS. 5-7;

FIG. 9 is a graph illustrating the deflection of a piezoelectricpolymorph used in the present invention with voltage applied thereto;

FIGS. 10-16 are diagrammatical sketches used to illustrate thefabrication of a valve plate used in the valve of FIG. 5,

FIGS. 10, 12, 15, and 16 being crosssectional views at various stages ofsuch fabrication,

FIG. 11 being a plan view of FIG. 10,

FIG. 13 being a plan view of a mask used in forming the structure shownin FIGS. 12, 14, 15, and 16, and

FIG. 14 being a plan view of FIG. 12.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

The present invention discloses a piezoelectric fluid control valve 10,an earlier embodiment of which is depicted in FIGS. 1 and 2. The valveincludes a valve body 12 with a supply port 14 for introducing hydraulicfluid into the valve at a supply pressure (P_(s)). In communication withthe supply port is a chamber 16 and an outlet port 18 which delivers thehydraulic fluid at a control pressure (P_(c)) to a device which isoperable in response to the control pressure. Such a device includes butis not limited to an anti-lock braking/traction control system, avehicular transmission system, an engine intake/outlet valve, and asuspension system. Patent application Ser. No. 07/765,613, now U.S. Pat.No. 5,217,283, entitled "Integral Anti-Lock Brake/Traction ControlSystem" was filed on Sep. 25, 1991 and is incorporated herein byreference. In general, it is contemplated that any application having amulti-stage valve can usefully be enhanced by the valve of the presentinvention as its first stage.

Supported within the chamber 16 is a top valve plate 22 and a bottomvalve plate 24. Each valve plate 22,24 has an anchored end 26,28 affixedto a wall of the chamber (not shown in FIG. 1 for simplicity) adjacentto the supply port 14. To permit fluid flow, the anchored end 26 of thetop valve plate 22 is provided with an inlet channel 30 (FIGS. 2-3)which is in communication with the supply port.

A metering orifice 40,42 is disposed within each valve plate 22,24.Seatable within each metering orifice is a double popper valve head 44which is continuously displaceable between an open position and anormally closed position. The valve head has sharp metering edges 46that cooperate with the associated metering orifice so that the edgesblock fluid flow when the valve head is seated.

Located within the chamber 16 is a polymorph, one embodiment of which isa bimorph 48 that preferably includes two piezoelectric ceramic wafers50,52 bonded together. Piezoelectric ceramics are known and have beenmarketed under such trade names as PXE (PIEZOXIDE) by N.V. Philips'Gloeilampenfabrieken, located in The Netherlands. Such materialsgenerally are compounds of lead zirconate and lead titanate.Piezoelectric crystals are polycrystalline ferrolectric materials withthe perovskite crystal structure -- a tetragonal/rhombahedral structurevery close to cubic. Piezoelectric properties are exhibited by a numberof naturally occurring crystals, such as quartz, tourmaline, and sodiumpotassium tartrate.

When two piezoelectric ceramic strips or wafers, polarized in theirthickness direction are bonded together, they form the bimorph 48. Ifthey are polarized in opposite directions, they become known as a seriesbimorph. If polarized in the same direction, they are known as aparallel bimorph.

As depicted in FIGS. 1-2, a piezoelectric ceramic beam, preferablycomprising wafers 50,52 is selected so that the wafers havepiezoelectric characteristics which are different. As a potentialdifference is applied across the wafers, one expands and the othercontracts, thereby bending the bimorph. Deflection is virtuallyinstantaneous and proportional to the potential difference.

Turning now to FIGS. 2-3, the anchored end 26 of plate 22 is providedwith an inlet channel 30 in communication with the supply port.

In an earlier embodiment of the invention, a double poppet valve head 44is seatable within metering orifices 40,42 provided within the valveplates 22,24. The valve head 44 is continuously displaceable between anopened position when the bimorph 48 bends and a normally closedposition. The double poppet valve head 44 has sharp metering edges 46that cooperate with the metering orifices 40,42, the edges blockingfluid flow when the popper valve head is seated.

To revert-the popper valve head to its normally closed position, meansfor biasing 54, such as a pair of springs, are affixed to the valveplates 22,24 and the double popper valve head. The biasing means alsoserve to register the popper valve head within the associated meteringorifice.

A voltage is applied to the bimorph 48, preferably by an electricalanalog charge-drive circuit 56 connected to the bimorph. The voltage isapplied in such a way that one wafer contracts while the other expands.Since the wafers are joined together, they bow.

Preferably, in a parallel bimorph configuration, both wafers arepolarized in the same direction and are connected in parallel. Thisoffers higher sensitivity and the possibility of applying a bias voltageto generate an electric field parallel to the direction of polarization,thus eliminating the risk of depolarization. Deflection in thisconfiguration is high, and blocking forces are relatively low.

The analog charge-drive circuit 56 applies a potential difference to thebimorph, which is regulated in accordance with an input signal deliveredto the circuit. The input signal is provided by an input signalgenerating means 58, such as a microprocessor in response to a parametercharacteristic of a sensed condition. For simplicity, details of themicroprocessor are omitted, as they fall within the purview of thoseskilled in the art. As an example, the microprocessor may generate theinput signal in response to a parameter such as wheel rotational speedsensed in a moving car. Input signals may also be generated in responseto other parameters sensed from brake pressure 300, wheel dynamics 302.

As an example, a plus 10 volts would open an hydraulic flow path fromthe supply pressure, increasing the control pressure on something suchas a mechanical brake in a vehicle. As the pressure increases, the forcethat the brake is applying on the vehicle will increase. A minus 10volts would then allow the hydraulic fluid to flow from the brake,reducing the amount of pressure or force that the brake is generating.

The analog charge-drive circuit exploits the fast response of high poweractuators. The circuit delivers high currents at high voltage levelsduring short periods. Essentially, the bimorph is a capacitive device.Accordingly, power levels can be considerable if the actuator isswitched at a high repetition rate.

Preferably, the bimorph is driven by a charge drive circuit in whichthere is a substantially linear relation between tip displacement andexcitation voltage (FIG. 9). That figure is an example of the deflectionof a piezoelectric actuator as a function of the applied voltage. Thecurves of FIG. 9 have been measured on a bimorph high power actuatorwhich is assembled from 9×18×1.0 mm rectangular plates.

Preferably, the analog charge drive circuit of the present inventiongenerates a current to the bimorph which causes a voltage drop across aresistor (not shown). This is used as a feedback signal for anoperational amplifier. The current to the bimorph, and thus the charge,is regulated according to the input voltage. This charge-drive circuitproduces a linear response between the input and output voltages.

It should be appreciated that though a polymorph has been disclosedherein, a configuration known as a monomorph may also be applicable. Ina monomorph, a ceramic element is bonded to a metal disk such that theconfiguration is planar in the absence of any potential differenceapplied across the ceramic element and metal disk. When a voltage isapplied opposite to poling, the piezoelectric ceramic expands. If thevoltage is applied in the direction of poling, the piezoelectric ceramicshrinks.

Turning now to FIG. 2, the top valve plate 22 is provided with a freeend 32 that defines an inlet channel 30 which is in communication withthe supply port. The associated fluid flows are depicted in FIGS. 2-3.The hydraulic fluid enters the valve body 12 at the supply port 14,whence it enters fluid inlet channel 30 toward the metering edges 46,which cooperate with the double popper valve head 44.

Preferably, the valve plates 22,24 are formed from silicon and themetering edges are formed by a technique such as that disclosed incommonly-owned, co-pending patent application Ser. No. 986,313, filed onDec. 7, 1992, now U.S. Pat. No. 5,309,943, entitled "MicroValve AndMethod Of Manufacture," the disclosure of which is incorporated hereinby reference. Preferably, the metering orifice provided within eachvalve plate is rectangular.

As illustrated in FIG. 2, biasing means 54 include a top spring 62extending between the free end of the top plate and the double poppervalve head, and a bottom spring 64 extending between the anchored end ofthe bottom valve plate and the double poppet valve head.

In operation, the bimorph 48 cooperates with the double popper valvehead 44 such that the latter is urged toward an open position when thebimorph is bent. In that configuration, the piezoelectric fluid controlvalve is opened and hydraulic fluid is allowed to flow toward the outletport 18.

A second-alternative embodiment of the present invention is depicted inFIG. 4. In that embodiment, the top and bottom valve plates 22,24 definea first pair of valve plates 66. A second pair 68 of valve plates isdisclosed in operative communication with the bimorph 48.

The second pair of valve plates 68 include a top valve plate 70 and abottom valve plate 72. The latter plate has an anchored end 74 that isprovided with an outlet channel 76 in communication with a return port78 defined within the valve body.

In the embodiment depicted in FIG. 4, the bimorph 48 is deflected uponapplying a potential difference thereto, so that the bimorph may movecontinuously towards a top deflected position, wherein the double poppetvalve head associated with the top pair of valve plates is opened, whilethe double popper valve head associated with the bottom pair of valveplates remains closed. From that position, the deflection of the bimorphmay revert to a normally closed position. FIG. 3 is a view of the valveillustrating the hydraulic path of FIG. 4.

When the bimorph is deflected downwardly, the double popper valve headassociated with the second pair of valve plates 68 is urged toward anopen position, away from its normally closed position against seatingforces exerted by a spring associated with the bottom valve plate 72 ofthe second pair 68. At the same time, the double popper valve headassociated with the first pair 66 is in its seated, normally closedposition, thereby occluding passage of the hydraulic fluid toward theoutlet port 18. As a result, the hydraulic fluid pressure from the valve(P_(c)) is continuously modulated in a linear relation with the inputsignal.

In one example, proportional control of the regulated pressure (P_(c))was demonstrated with a conventional solenoid valve. The fluid flow ratewas measured at 2.6 cubic inches per second maximum and P_(c) was about1500 psi. The normal range of fluid flow was up to 0.52 cubic inches persecond.

A third embodiment of the piezoelectric fluid control valve of thepresent invention is depicted schematically in FIGS. 5-8. FIG. 5 depictsthe valve in an "apply" or "build" position; FIG. 6 depicts the valve ina "dump" position; and FIG. 7 depicts the valve in a "closed" position.

In FIGS. 5-8, an upper metering element 100 may include a top valveplate 112 and a contiguous bottom valve plate 114. A lower meteringelement 116 also may include a top 118 and bottom 120 valve plate. Inpractice, valve plates 112, 114 may be an integral unit. A similarobservation is also applicable to plates 118, 120.

Each metering element 100, 116 has an anchored end affixed to the wallsof the chamber 16, as shown. The anchored end of the upper meteringelement 100 is provided with an inlet channel 122, as shown. An outletchannel 123 is defined within the lower metering element 116. A pair ofmetering orifices 124, 126 is provided within each metering element 100,116, respectively, as shown. A cantilevered spring valve 128, 130 ispositionable within the associated metering orifice 124, 126,respectively, as shown. Each cantilevered spring valve 128, 130 iscontinuously displaceable between an opened position (see FIG. 5 of theupper metering element 100), and a normally closed position (see, e.g.,cantilevered spring valve 130 of the lowering metering element 116depicted in FIG. 5). Each one of the cantilevered spring valves 128, 130has sharp metering edges 131, 133 that cooperate with each other toprovide the associated metering orifices 124, 126, the edges 131, 133blocking fluid when the cantilevered spring valves 128, 130 are closed.

Positioned between the cantilevered spring valves 128, 130 is thepolymorph 132 which is in operative communication with the upper 100 andlower 116 metering elements. When a potential difference is applied by acircuit such as that depicted in FIGS. 2 and 4, the polymorph 132becomes deflected in proportion to the potential difference.

In FIG. 6, the polymorph 132 is depicted in a downwardly deflectedposition in response to a potential difference generated in anelectrical circuit (not shown). In the valve configuration depicted inthat figure, hydraulic flow is diverted to the return port 78.

FIG. 7 depicts the valve in its closed position, wherein the polymorph132 is in a null or undeflected position. In that position, the meteringorifices 124, 126 are closed, so that the inlet and outlet channels 122,123 are occluded.

FIG. 8 illustrates that in the third embodiment, each cantileveredspring valve has three sides of a rectangle so that each cantileveredspring valve effectively acts as a single piece "flapper." In the thirdembodiment, the double popper valve and spring of the earlier disclosedembodiment are combined in a single "flap."

FIG. 9 graphically illustrates a relatively large deflection obtained bythe polymorph 132 as a result of the application of various appliedvoltages. Experimentally, the curve of FIG. 9 was derived with anoptical non-contacting sensor. Such experiments have shown that it ispossible to displace the cantilevered spring valves under load up toabout 100 times per second. In the absence of any load, the polymorphmay be displaced as quickly as about 2000 times per second. Suchperformance characteristics represent a quantum improvement over an artin which solenoid actuators respond at rates which are about 50% slower.

Current steel valves that are high precision and hand made tend toperform within a 100 hertz bandwidth, with a solenoid actuator capableof operation at 850-900 hertz. The polymorph exhibits a 2000 hertzbandwidth.

The polymorph to which the previous experimental procedure was subjectedmeasured 18×9×1 mm, of which about 3.5 mm were rigidly mounted.

In light of the previous disclosure, it will be apparent that if apressure transducer is in operative communication with the valve of thepresent invention, a pressure control valve would result.

It is first noted that the valve plates 112, 114, 116, 118 aresubstantially the same. Thus, referring now to FIGS. 10-15, the methodfor forming an exemplary one of the valve plates 112, 114, 116, 118,here plate 112 will be described. Referring first to FIGS. 10 and 11, asemiconductor body 200, here lightly doped silicon having aconcentration of 10¹⁶ /cm³ and a surface 202 parallel to the <100>crystallographic plane, is provided. The upper and lower surfaces arepolished. A more heavily doped layer 240, here 10 microns thick, isformed over the surface 202 by diffusing or implanting a P+type dopant(here boron) into the surface 202, or by epitaxially growing such borondoped layer 240 on the surface 202. Here, the concentration of the borondopant is 7×10¹⁹ /cm³ in layer 240. The thickness of the silicon body200 is here 340 microns.

Next, a layer of silicon dioxide 242 is chemically vapor deposited onthe upper surface of the doped layer 240, as shown in FIG. 10. It shouldbe noted that the thickness of layer 242 is here 2 micrometers. Windows246, 248 are reactive ion etched with vertical sidewalls into silicondioxide layer 242 and into the doped layer 240, as shown, usingconventional photolithographic etching processes. It is first noted thatwindow 248 is formed to have three sides of a rectangle which correspondto the orifice 124 (FIG. 8) and window 246, here square, corresponds tosupply port 14 (FIG. 8). In a typical embodiment the length and width ofthe rectangle are here 10 mm by 10 mm. It is next noted that the window248 here has a width in the order of 1 micrometer and the window 246 hasa width substantially larger, here several millimeters. Next, thesilicon dioxide layer 242 is removed using a buffered hydrofluoric acidsolution.

Next, layer 250_(T), and 250_(b) of silicon nitride are chemically vapordeposited over the upper surface of the doped layer 240 and the bottomsurface 252 of the silicon body 200, respectively. Here, thickness ofthe silicon nitride layers 250_(T), 250_(B), is 0.1 micrometers, asshown in FIG. 12. A layer of photoresist, not shown is deposited overthe bottom silicon nitride layer 250_(B). A mask 254, shown in crosshatch in FIG. 13, having an aperture 256 formed therein is imaged ontothe photoresist layer, not shown, in a conventional manner. It is firstnoted that region 258 of aperture 256 is used to form the lower portionof supply port 14 (FIG. 8). Regions 260 are used to form inlet channels122 (FIGS. 5 and 8). The portion 262 of the aperture 256 is used to formthe region below the metering orifice 124 (FIGS. 5-8). The exposedportions of the silicon nitride layer 250_(B) exposed by aperture 256are removed using a conventional reactive ion etching process to form awindow 264 therein corresponding to aperture 256.

Next, the photoresist layer, not shown, is removed or stripped in aconventional manner. Referring now to FIGS. 12, 14, and 15, the bottomportions of the silicon body 200 exposed by the window 264 now formed inthe silicon nitride layer 250_(B) are removed using a preferential oranisotropic etchant, here a solution of potassium hydroxide andisopropyl alcohol. More particularly the structure is submerged in abath of such solution. It is noted that because of the crystallographicaxis orientation of the silicon body 200, there is substantially noundercutting of the portions of the silicon body 200 disposed under thesilicon nitride layer 250_(B). The etchant proceeds at an acute angle,here 54.7°. It is further noted, however, that because of the fact thatthere will be some undercutting around the corners of the maskingwindows, mask compensation, not shown, may be used at the corners 266 ofthe mask 254 (FIG. 13) to account for such undercutting.

The silicon nitride layer 250_(T) is used to protect the upper portionof the metering orifice 124 (FIGS. 8, 12, 14, and 15) from erosion bythe solution of potassium hydroxide and isopropyl alcohol. The dopedsilicon layer 240 prevents erosion of the bottom surface of the meteringorifice 124 by the solution of potassium hydroxide and isopropyl alcoholbecause such layer 240 etches at a much lower rate than silicon body200. It is also noted that the region 262 (FIG. 13) of the mask 254 iswider than the width of region 260. Thus, the depth of etching into thebottom surface of the silicon body 200 is greater under region 262(i.e., under the metering orifice 124 and port 14 (FIG. 12)) than underregion 260 (i.e., the channels 122 (FIGS. 8, 12, 14, 15)). Next, thesilicon nitride layers 250_(T), 250_(B) are removed using phosphoricacid to produce the valve plate 112 as shown in FIG. 16. It is notedthat edges of doped silicon layer 240 forming orifice 124 do not contacteach other. However, the orifice 124 is less than, or equal to, 1 micronand thus provide sufficient fluid blockage because of the viscosity andsurface tension of the fluid.

Thus, valve plate 112 includes a semiconductor body, here silicon body200, including doped layer 240, having formed integrally therein acantilevered member, here cantilevered spring valve or flapper 128. Theproximate end 231 of flapper 128 is integrally formed with thesemiconductor body 200 and doped layer 240. Thus, an electro-mechanicalactuator, here polymorph 132, deflects flapper 128 about axis 270. Inparticular, polymorph 132 deflects the distal end 272 of flapper 128relative to the fixed, surrounding portions 281 of the supportingsemiconductor body 200 and doped layer 240 in response to electricalsignals fed to the polymorph 132 (FIG. 5).

Each one of the metering elements includes a pair of valve plates, suchas plate 112, with their bottom surfaces bonded together, as shown inFIGS. 5-7. The polished mating surfaces of each plate are opticallycontacted and bonded together using conventional direct wafer bondingtechniques.

Referring again to FIG. 7, it is first noted that the spring valve 128is shown in the closed position. In such condition, the fluid in region301 exerts equal and opposite forces on surfaces 300, 302, respectively.In addition, in the closed condition, fluid in regions 310, 320 exertforces on surfaces 304, 306 of the spring valve 128 which are also equaland opposite forces. It is noted that regions 310, 320 are withinchamber 16 and thus are always at the same pressure. Thus, the valve 128is statically pressure balanced by fluid in region 301 and regions 310,320. In response to an electrical signal, the polymorph 132 deflects thespring valve 128 as shown in FIG. 5, for example. The force required bythe polymorph 132 to deflect such valve 128 must be sufficient toovercome only the mechanical stiffness of the spring valve 128 becauseof the static pressure balance provided by the surrounding fluid inregions 301, 310 and 320. The stiffness of the valve 128 provides arestoring force against the dynamic fluid forces that may arise fromfluid flowing through the opened valve. Likewise, to close the valve128, the only force required is that which is necessary to overcome thedynamic fluid forces. Forces exerted at opposing edges help to create acounterbalancing effect which contributes to the high frequency responseof the device.

Thus, there has been disclosed a piezoelectric fluid control valve whichexhibits a higher frequency response than presently known. The valveprovides a continuous modulation of fluid pressure in a linearrelationship with the input signal communicated to the valve.Additionally, a preferred embodiment of the valve of the presentinvention can be fabricated at a relatively low cost in productionquantities because it has only three moving parts: cantilevered springvalves 128, 130 and polymorph 132. Furthermore, a polymorph may bemounted to each surface of each valve 128 of elements 100, 116.

It is understood, therefore, that having described preferred embodimentsof the invention, it will now be apparent to one of skill in the artthat other embodiments incorporating its concept may be used. It isbelieved, therefore, that this invention should not be restricted to thedisclosed embodiments, but rather should be limited only by the spiritand scope of the appended claims.

We claim:
 1. A method for controlling fluid delivered to a device driventhereby, the method comprising:delivering the fluid into a supply portdisposed in a valve body, the valve body including an outlet portcapable of delivering the fluid to the device, and a relief port forreturning the fluid to a source thereof; positioning a polymorphsandwiched between an upper and a lower metering element, the polymorphand the metering elements being supported by a wall of the valve body,one of the metering elements being provided with an inlet channel, andthe other metering element being provided with an outlet channel;providing a pair of opposing metering orifices within each meteringelement; disposing a cantilevered spring valve within each pair ofmetering orifices, each cantilevered spring valve being continuouslydisplaceable between an opened position and a normally closed position,each cantilevered spring valve having a pair of metering edges thatcooperate with the associated metering element so that the edges blockfluid when the associated cantilevered spring valve is closed; applyinga potential difference through an electrical circuit across thepolymorph, thereby deflecting the polymorph in proportion to thepotential difference so that one of the cantilevered spring valves isdisplaced and fluid is communicated from the source of the fluid to theoutlet port of the valve body, the potential difference being regulatedin accordance with an input signal delivered to the electrical circuit;and communicating a means for generating the input signal to theelectrical circuit, the input signal being generated in response to asensed condition so that fluid delivered to the device through theoutlet port is continuously modulated in response to the sensedcondition.
 2. The method of claim 1, wherein the sensed condition isbrake pressure.
 3. The method of claim 1, wherein the sensed conditionis wheel dynamics.
 4. The method of claim 1, wherein the step ofcommunicating a means for generating the input signal to the electricalcircuit is performed for the purpose of controlling wheel decelerationduring a braking maneuver.
 5. The method of claim 1, wherein the methodfurther comprises:communicating an anti-lock braking system to theoutlet port of the valve body.
 6. A method for controlling fluiddelivered to a device driven thereby, the method comprising:deliveringthe fluid into a supply port disposed in a valve body, the valve bodyincluding an outlet port capable of delivering the fluid to the device,and a relief port for returning the fluid to a source thereof;positioning a polymorph sandwiched between an upper and a lower meteringelement, the polymorph and the metering elements being supported by awall of the valve body, one of the metering elements being provided withan inlet channel, and the other metering element being provided with anoutlet channel; providing a pair of opposing metering orifices withineach metering element; disposing a cantilevered spring valve within eachpair of metering orifices, each cantilevered spring valve beingcontinuously displaceable between an opened position and a normallyclosed position, each cantilevered spring valve having a pair ofmetering edges that cooperate with the associated metering element sothat the edges block fluid when the associated cantilevered spring valveis closed; applying a potential difference through an electrical circuitacross the polymorph, thereby deflecting the polymorph in proportion tothe potential difference so that one of the cantilevered spring valvesis displaced and fluid is communicated from the outlet port to therelief port, the potential difference being regulated in accordance withan input signal delivered to the electrical circuit; and communicating ameans for generating the input signal to the electrical circuit, theinput signal being generated in response to a sensed condition so thatfluid delivered to the device through the outlet port is continuouslymodulated in response to the sensed condition.
 7. A method forcontrolling fluid delivered to a device driven thereby, the methodcomprising:delivering the fluid into a supply port disposed in a valvebody, the valve body including an outlet port capable of delivering thefluid to the device, and a relief port for returning the fluid to asource thereof; positioning an actuator sandwiched between an upper anda lower metering element, the actuator and the metering elements beingsupported by a wall of the valve body, one of the metering elementsbeing provided with an inlet channel, and the other metering elementbeing provided with an outlet channel; providing a pair of opposingmetering orifices within each metering element; and disposing acantilevered spring valve within each pair of metering orifices, eachcantilevered spring valve being continuously displaceable between anopened position and a normally closed position, each cantilevered springvalve having a pair of metering edges that cooperate with the associatedmetering element so that the edges block fluid when the associatedcantilevered spring valve is closed.
 8. A method for controlling fluiddelivered to a device driven thereby, the method comprising:deliveringthe fluid into a supply port disposed in a valve body, the valve bodyincluding an outlet port capable of delivering the fluid to the device,and a relief port for returning the fluid to a source thereof;positioning an actuator sandwiched between an upper and a lower meteringelement, the actuator and the metering elements being supported by awall of the valve body, one of the metering elements being provided withan inlet channel, and the other metering element being provided with anoutlet channel; providing a pair of opposing metering orifices withineach metering element; disposing a cantilevered spring valve within eachpair of metering orifices, each cantilevered spring valve beingcontinuously displaceable between an opened position and a normallyclosed position, each cantilevered spring valve having a pair ofmetering edges that cooperate with the associated metering element sothat the edges block fluid when the associated cantilevered spring valveis closed; applying a potential difference through an electrical circuitacross the actuator, thereby deflecting the actuator in proportion tothe potential difference so that one of the cantilevered spring valvesis displaced and fluid is communicated to a port, the potentialdifference being regulated in accordance with an input signal deliveredto the electrical circuit; and communicating a means for generating theinput signal to the electrical circuit, the input signal being generatedin response to a sensed condition, so that fluid delivered to the devicethrough the outlet port is continuously modulated in response to thesensed condition.
 9. A method for controlling fluid delivered to adevice driven thereby, the method comprising:delivering the fluid into asupply port disposed in a valve body, the valve body including an outletport capable of delivering the fluid to the device, and a relief portfor returning the fluid to a source thereof; positioning an actuatorsandwiched between an upper and a lower metering element, the meteringelements each having a peripheral edge which is supported by a wall ofthe valve body, the actuator and the metering elements being supportedby a wall of the valve body one of the metering elements being providedwith an inlet channel, and the other metering element being providedwith an outlet channel; providing a pair of opposing metering orificeswithin each metering element; and disposing a cantilevered spring valvewithin each pair of metering orifices, each cantilevered spring valvebeing continuously displaceable between an opened position and anormally closed position, each cantilevered spring valve having a pairof metering edges that cooperate with the associated metering element sothat the edges block fluid when the associated cantilevered spring valveis closed.